1. Technical Field
This invention relates to a control circuit suitable for a program shutter permitting a shutter blade to be opened and closed by a step motor.
2. Prior Art
The program shutter permitting a shutter blade to be opened and closed by the step motor is constituted in such that a drive pulse having a fixed frequency is inputted to the step motor by a release operation to forwardly rotate the step motor and gradually open sectors, and a phase of the drive pulse is switched at a timing when the step motor is rotated by such steps as corresponding to an exposure quantity to reversely rotate the step motor and close the sectors, thus obtaining a predetermined exposure.
However, as the step motor to be used for the shutter has a low maximum rotating speed of at most 500-1000 pulse/sec, a shortest time required for rotation of one step is limited, and in particular, there occurs large error in short time exposure. On the other hand, there occurs slippage between a drive signal and an exposure quantity due to ununiformity of a sector shape and play of a rotation transmitting mechanism, etc. As a result, it has been impossible to obtain an expected exposure.